The present invention deals with the nuclear camera arts. It finds particular application in conjunction with electronics used in SPECT cameras and will be described with particular reference thereto. However, it is to be appreciated that the present invention may find application in PET cameras and other radiation detection systems in which high voltage biases are applied to detector arrays.
Nuclear imaging employs a source of radioactivity to image the anatomy of a subject. Typically, a radiopharmaceutical is injected into the patient. This source contains atoms that decay at a predictable rate. Each time an atom decays, it releases a xcex3-ray. These xcex3-rays are detected, and from information such as its position and energy, a representation of the interior of the subject is reconstructed.
Typically, a nuclear camera has one, two, or three detector heads. Each head has a large scintillator sheet, such as doped sodium iodide, which converts incident radiation into scintillations, i.e. flashes of light. An array of photomultiplier tubes is disposed in back of the scintillator to monitor for light flashes. The output of the photomultiplier tubes and associated circuitry indicates the coordinates of each scintillation on the sodium iodide crystal and its energy. Unfortunately, there are numerous non-uniformities and inaccuracies when using a large scintillator crystal and an array of photomultiplier tubes.
Rather than using a single, large scintillator and photomultiplier tubes, others have proposed using an array of small scintillators, each associated with a photodiode or other photoelectrical device which senses a scintillation in each individual scintillation crystal. Other types of individual solid-state detectors have also been suggested.
Solid state radiation detectors utilize the photoelectric effect to detect radiation. That is, received radiation photons liberate electrons from their orbits around atoms of the target material. The electrons are detected as an electrical signal. Electrons released by a single photon typically generate a weak signal that is amplified. Typically, a high bias voltage is applied across the detector material to aid the photoelectric phenomenon. These voltages typically are several hundreds of volts. With such high biases, these systems become sensitive to electrical noise, and ambient photoelectric radiation, such as visible light. Because of this sensitivity, noise in the bias or stray light/radiation can be mistaken for events for which the detector is looking.
The present invention provides a new and improved method and apparatus that overcomes the above referenced problems and others.
In accordance with one aspect of the present invention, a nuclear imaging apparatus is given. A detector system detects xcex3-rays and generates electrical signals in response. A Faraday cage shields the detector system. Downstream electronics process the electrical signals that the detector system generates, and a reconstruction processor reconstructs the electrical signals into an image representation.
In accordance with another aspect of the present invention, a nuclear camera is given. A plurality of solid state arrays respond to incoming xcex3-irradiation by releasing electrons. Conductive strips provide a bias to the arrays. Conductive pads lie opposite the conductive strips. A voltage source supplies power to the conductive strips, setting up an electric field, attracting electrons to the conductive pads. Signal processing circuitry provides information about electronic activity to a reconstruction processor that processes the data into an image representation.
In accordance with another aspect of the present invention, a radiation detector assembly is given. An array of detectors that detects high energy radiation is biased by a bias circuit that applies a high voltage potential between opposite faces of the detector array. An electrically insulating layer and a ground layer are mounted on a radiation receiving side of the bias circuit. High-z metal vanes collimate incumbent radiation.
In accordance with another aspect of the present invention, a method of nuclear imaging is given. A bias voltage is applied to a solid state detector array, and is filtered to remove noise. Response is given to incident radiation by generating a current pulse. The current pulses are processed and reconstructed into an image representation.
One advantage of the present invention is that it allows for accurate detection of radiation events.
Another advantage of the present invention is that reduces noise in large bias voltages.
Yet another advantage of the present invention is that it reduces the chance of the system being affected by ambient photoelectric radiation.
Yet another advantage of the present invention is the ease of assembly of the detector system and disassembly for servicing the system.
Still further benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.